Yahoo! Finance
You may hate bills and junk mail, but you'll probably never complain about either again if you receive an audit letter. As you likely are keenly aware, an audit letter is a piece of correspondence that no taxpayer wants to receive in the mail, and it means that the Internal Revenue Service wants to get to know you a little better. But instead of chit-chatting over coffee like old friends, your pals at the IRS want to examine your tax records for the last three years. If they really want to get to know you well, they might ask for six years' worth of records. But they won't go further back than that, according to the IRS website.